Method for manufacturing polarizing film and polarizing film and optical film manufactured by using the method

ABSTRACT

A polarizing film is provided that prevents display unevenness and can form a liquid crystal display and an electroluminescence display that exhibit excellent display characteristics. The polarizing film is produced in the following manner. That is, a hydrophilic polymer film is conveyed by means of a guide roll so as to be impregnated in an aqueous solvent in a swelling bath and is allowed to swell. In this swelling step, at least a first guide roll is arranged in the swelling bath, and when the polymer film is impregnated in and allowed to travel in the aqueous solvent, the polymer film is brought into contact with the first guide roll within a time up to when swelling reaches a saturation state. Further, the polymer film is dyed using a dichroic substance and stretched.

TECHNICAL FIELD

The present invention relates to a method of producing a polarizingfilm, a polarizing film produced by the method and an optical film.

BACKGROUND ART

Liquid crystal displays (LCDs) have been used widely, for example, fordesk calculators, electronic clocks, personal computers, wordprocessors, and instruments of automobiles and machines. Generally, sucha liquid crystal display includes a polarizing plate for visualizing avariation in orientation of its liquid crystal, and the polarizing platehas an extremely large influence on display characteristics of theliquid crystal display.

As the polarizing plate, for example, a laminate formed in the followingmanner is used commonly. That is, a polarizer (polarizing film) such asa polyvinyl alcohol (PVA)-based film or the like is made to absorb adichroic substance such as iodine, an organic dyestuff or the like andis aligned, and a protective film made from triacetylcellulose or thelike is laminated on each surface of the polarizer. Particularly, therehas been a demand for a polarizer that allows a liquid crystal displayto have high brightness, good color reproducibility and excellentdisplay characteristics.

However, in the liquid crystal display, particularly, in the case ofusing a backlight that emits polarized light, display unevenness occursto decrease contrast uniformity, which has been disadvantageous.Particularly, in an image display, the achievement of high contrastentails a considerable degree of such display unevenness. For example,in the case where a normally black mode (in which a black display stateis established in a state where no voltage is applied) is established asa liquid crystal mode, a considerable degree of display unevenness isobserved in the view from an oblique direction at an angle of at least30°, 40° and 60°.

Meanwhile, a polarizer is produced generally by the following method.That is, a hydrophilic polymer film is conveyed by means of a guide rollso as to be impregnated in a swelling bath for swelling, then isimpregnated in a dyebath containing a dichroic substance for dyeing, andfurther is stretched while being impregnated in a crosslinking bath.Previously, for example, JP2002-28939 A and JP2002-31720 A havedisclosed as the hydrophilic polymer film PVA films having improvedthickness uniformity. However, even when such a film is used, there is apossibility that a polarizer as a finished product has a variation inretardation and a variation in the content of a dichroic substance.

DISCLOSURE OF THE INVENTION

For the reasons described above, the object of the present invention isto provide a polarizing film for use in various types of displays thatfurther prevents the occurrence of display unevenness and exhibitsuniform display characteristics.

In order to achieve the above-mentioned object, as a method of producinga polarizing film according to the present invention, first and secondproduction methods are provided as follows.

That is, the first production method according to the present inventionis a method of producing a polarizing film comprising the steps of:allowing a hydrophilic polymer film to swell wherein the polymer film isconveyed by means of a guide roll so as to be impregnated in an aqueoussolvent in a swelling bath; dyeing the polymer film using a dichroicsubstance; and stretching the polymer film. In the method, in theswelling step, at least one guide roll (first guide roll) is arranged inthe swelling bath, and when the polymer film is impregnated in andallowed to travel in the aqueous solvent, the polymer film is broughtinto contact with the guide roll (first guide roll) within a time up towhen swelling reaches a saturation state.

Furthermore, the second production method according to the presentinvention is a method of producing a polarizing film comprising thesteps of: allowing a hydrophilic polymer film to swell in an aqueoussolvent, in which the film is conveyed by means of a guide roll so as tobe impregnated in a swelling bath of the aqueous solvent; dyeing thefilm using a dichroic substance; and stretching the film. In the method,in the swelling step, at least one guide roll (first guide roll) isarranged in the swelling bath, and when the film is impregnated in andallowed to travel in the aqueous solvent, the film is brought intocontact with the guide roll (first guide roll) after swelling reaches asaturation state.

In order to achieve the above-mentioned object, the inventors of thepresent invention conducted a vigorous study on the production of apolarizing film. The study led them to the following findings. That is,when a polyvinyl alcohol (PVA) film that is a hydrophilic polymer filmis impregnated in an aqueous solvent in a swelling bath, generally,swelling occurs abruptly within 15 seconds to 25 seconds. If the PVAfilm is brought into contact with a guide roll at that point in time,wrinkles may be formed in the film on the surface of the guide roll.This causes the PVA film to have a variation in retardation and furtherto have a variation in the content of a dichroic substance. Theinventors found that the above-mentioned problems, i.e. a variation inretardation and a variation in the content of a dichroic substance couldbe reduced in the following manner. That is, a point in time at whichthe polymer film is brought into contact with the guide roll iscontrolled according to the swollen state of the polymer film.Specifically, a length of time between the time when the hydrophilicpolymer film is brought into contact with the aqueous solvent in theswelling bath and the time when the polymer film is bought into contactwith the guide roll in the swelling bath is controlled. The inventorsthus arrived at the above-described first and second methods ofproducing a polarizing film. Further, conceivably, the formation ofwrinkles is attributable to slack caused by a phenomenon in which, inthe swelling step, a thin portion of a polymer film is stretched byswelling to a greater degree than in other portions thereof.Conventionally, this problem has been solved by performing a stretchingtreatment. However, when wrinkles are smoothed by the stretchingtreatment, for example, there are possibilities that a dichroicsubstance is absorbed in a less amount, and that the dichroic substanceis desorbed in a later step (for example, a crosslinking step). This mayresult in the occurrence of a considerable degree of dyeing unevenness,which has been disadvantageous. On the other hand, according to themethod of the present invention, instead of performing a stretchingtreatment in order to smooth wrinkles, the formation of wrinkles itselfis reduced, and thus the conventional problems also can be avoided.Incidentally, the inventors of the present invention were the first todetermine that the relationship between a film and a guide roll exerts alarge influence on the formation of wrinkles and dyeing unevenness of apolarizing film to be produced.

According to the above-described first and second production methods ofthe present invention, in a polarizing film to be obtained, a variationin retardation and a variation in the content of a dichroic substanceare suppressed. Therefore, when applied to, for example, various typesof image displays such as a liquid crystal display and the like,particularly, large-sized or high-contrast displays, and flat paneldisplays, the polarizing film has the effect that display unevenness(particularly, display unevenness in black display) can be eliminatedsufficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an example of a swelling step in amethod of producing an optical film according to the present invention.

FIG. 2 is a schematic diagram showing another example of the swellingstep in the method of producing an optical film according to the presentinvention.

FIG. 3 is a schematic diagram showing examples of a guide roll that isused in the production method according to the present invention.

FIG. 4 is a cross-sectional view showing an example of an optical filmaccording to the present invention.

FIG. 5 is a cross-sectional view showing another example of the opticalfilm according to the present invention.

FIG. 6 is a cross-sectional view showing an example of a liquid crystalpanel according to the present invention.

FIG. 7 is a cross-sectional view showing another example of the liquidcrystal panel according to the present invention.

FIG. 8 shows in (A) a cross-sectional view showing still another exampleof the liquid crystal panel according to the present invention, and (B)and (C) are partial cross-sectional views of (A).

FIG. 9 is a cross-sectional view of an example of a backlight used inExamples of the present invention.

FIG. 10 is a cross-sectional view of another example of the backlightused in the Examples of the present invention.

FIG. 11 is a cross-sectional view of still another example of thebacklight used in the Examples.

FIG. 12 shows in (A) a cross-sectional view of a yet still anotherexample of the backlight used in the Examples, and (B) schematicallyshows a partial view of (A).

BEST MODE FOR CARRYING OUT THE INVENTION

The description is directed first to the first production methodaccording to the present invention. As described above, the firstproduction method according to the present invention is a method ofproducing a polarizing film comprising the steps of: allowing ahydrophilic polymer film to swell wherein the polymer film is conveyedby means of a guide roll so as to be impregnated in an aqueous solventin a swelling bath; dyeing the polymer film using a dichroic substance;and stretching the polymer film. In the method, in the swelling step, atleast a first guide roll is arranged in the swelling bath, and when thepolymer film is impregnated in and allowed to travel in the aqueoussolvent, the polymer film is brought into contact with the first guideroll within a time up to when swelling reaches a saturation state.Further, preferably, the polymer film is brought into contact with thefirst guide roll within a time up to when swelling of the polymer filmreaches saturation and before the swelling occurs abruptly.

In the first production method according to the present invention, it isonly required that the polymer film is brought into contact with thefirst guide roll within a time up to when swelling reaches saturation.There is no particular limitation on a required length of time (a)between the time when the polymer film is brought into contact with theaqueous solvent and the time when the polymer film is brought intocontact with the first guide roll, and also can be determinedappropriately according to, for example, the temperature for theswelling bath. Specifically, it is preferable that the required lengthof time (a) is 0.6 seconds to 12 seconds for the following reason. Thatis, generally, swelling of a polymer film occurs abruptly within 15seconds to 25 seconds as described above, and thus in the case where therequired length of time (a) is 0.6 to 12 seconds, after the polymer filmis brought into contact with the first guide roll, swelling of thepolymer film occurs abruptly and reaches saturation, so that theformation of wrinkles is suppressed. Thus, in a polarizing film as afinished product, a variation in retardation and a variation in thecontent of a dichroic substance can be suppressed. The required lengthof time (a) is in the range of, preferably, 1.2 seconds to 9 seconds,and more preferably, 2.5 seconds to 7 seconds.

Furthermore, the required length of time (a) can be determinedappropriately according to, for example, the temperature for a swellingbath. It is particularly preferable that the required length of time (a)is in the range of 2.5 to 4 seconds when the temperature for theswelling bath is 40° C. to 50° C., in the range of 2.5 to 6 seconds whenthe temperature is 30° C. to lower than 40° C., and in the range of 2.5to 7 seconds when the temperature is 15° C. to lower than 30° C.

In the first production method according to the present invention,preferably, in the case where a second guide roll further is arranged inthe swelling bath, the polymer film is brought into contact with thefirst guide roll within a time up to when swelling reaches saturationand further is brought into contact with the second guide roll after theswelling reaches saturation for the following reason. That is, in thismanner, for example, the formation of wrinkles attributable to thepolymer film being brought into contact with the first guide roll can besuppressed, and after being brought into contact with the first guideroll, the polymer film is allowed to swell to saturation, therebyreceiving no influence even when brought into contact next with thesecond guide roll. When the polymer film is brought into contact withthe second guide roll, it is not necessarily required that swelling ofthe polymer film have reached a saturation state as long as the swellinghas already occurred abruptly.

A required length of time (b) between the time when an arbitrary pointon the polymer film is brought into contact with the first guide rolland the time when the point is brought into contact with the secondguide roll is in the range of, for example, preferably 13 seconds to 120seconds, more preferably 20 to 100 seconds, and particularly preferably33 seconds to 80 seconds. Further, a total length of time of therequired length of time (a) and the required length of time (b) is, forexample, preferably in the range of 25 to 180 seconds, more preferably30 to 160 seconds, and particularly preferably 40 to 140 seconds.

Furthermore, similarly to the required length of time (a), the requiredlength of time (b) can be determined appropriately also according to thetemperature for a swelling bath. It is particularly preferable that therequired length of time (b) is in the range of 15 to 80 seconds when thetemperature for the swelling bath is 40° C. to 50° C., in the range of20 to 85 seconds when the temperature is 30° C. to lower than 40° C.,and in the range of 25 to 90 seconds when the temperature is 15° C. tolower than 30° C.

FIG. 1 is a diagrammatic view showing an example of a swelling step inthe first production method according to the present invention. As shownin the figure, two guide rolls 41 and 42 are arranged externally to aswelling bath 32, and two guide rolls 43 and 44 are arranged inside theswelling bath 32. The swelling bath 32 is filled with an aqueous solvent33. The guide rolls are arranged in order along the traveling directionof a polymer film (direction indicated by an arrow in the figure), and,among the guide rolls arranged in the swelling bath 32, the one arrangedupstream in the traveling direction of the polymer film serves as thefirst guide roll 43, and the other serves as the second guide roll 44.When a polymer film 31 is conveyed by means of the guide rolls, thelength between a part of the polymer film 31 that is brought intocontact with the aqueous solvent (namely, the surface of the aqueoussolvent) and a part of the polymer film 31 that is brought into contactwith the first guide roll 43 is defined as a length [a], and the timerequired for an arbitrary point on the polymer film 31 to travel thelength a is defined as a required length of time (a). Further, thelength between the part of the polymer film 31 that is brought intocontact with the first guide roll 43 and a part of the polymer film 31that is brought into contact with the second guide roll 44 is defined asa length [b], and the time required for an arbitrary point on thepolymer film 31 to travel the length b is defined as a required lengthof time (b). There is no particular limitation on the number of guiderolls to be arranged, and an additional guide roll further may bearranged inside or externally to a swelling bath as required.

In the case of using the above-mentioned swelling bath, firstly, thepolymer film 31 is conveyed by means of the guide rolls from the outsideof the swelling bath 32 (the left side in the figure) into the swellingbath so as to be impregnated in the aqueous solvent 33. Then, within atime up to when swelling of the polymer film 31 reaches saturation, thepolymer film 31 is allowed to travel the length [a], and within a timeup to when the polymer film 31 traveling from the first guide roll 43reaches the second guide roll 44, the polymer film 31 is allowed toswell to saturation. As for the required length of time (a) and therequired length of time (b), reference should be made to the abovedescription.

The length a between a part of the polymer film that is brought intocontact with the aqueous solvent 33 in the swelling bath 32 and a partof the polymer film that is brought into contact with the first guideroll 43 is not particularly limited, and is in the range of, forexample, 4 to 2,400 mm. The length [b] between a part of the polymerfilm 31 that is brought into contact with the first guide roll 43 and apart of the polymer film 31 that is brought into contact with the secondguide roll 44, namely, the distance between the first guide roll 43 andthe second guide roll 44 is not particularly limited, and is in therange of, for example, 80 to 36,000 mm. Further, the speed at which thefilm is conveyed is, for example, 6 to 200 mm/sec.

There is no particular limitation on the type of the guide rolls, andconventionally known types of guide rolls can be used. Examples of suchguide rolls are shown schematically in FIG. 3. In the figure, (a) showsa flat roll with a surface having no unevenness, (b) shows a crown rollthat is effective in smoothing wrinkles, (c) shows an expander roll, (d)shows a roll with lugs, and (e) shows a spiral roll. Alternatively, abent roll and the like also can be used. Among these, as also describedin JP2000-147252 A, preferably, a spiral roll is used as a guide rollother than the first guide roll because of the possibility of leavingdepressions on a hydrophilic polymer film (this also applies to thesecond production method). Further, the guide rolls preferably exhibitthe effect of smoothing wrinkles, and preferably, the effect is suchthat the film is not stretched in a lateral direction to a degreegreater than the degree to which the film is stretched by swelling in awidth direction. Specifically, assuming that the length in the widthdirection of the film after being stretched by swelling is defined to be100%, the rate at which the film further is stretched by the guide rollsis, for example, preferably 20% or lower, more preferably 10% or lower,and still more preferable 5% or lower.

The material for the above-mentioned types of rolls is not particularlylimited and can be, for example, metal or a polymer. However,preferably, an expander roll, at least a lug portion of a roll withlugs, and a spiral roll are formed from, for example, a material havingsurface energy almost equivalent to surface energy of the film beingtreated in the swelling bath.

The description is directed next to the second production methodaccording to the present invention. As described above, the secondproduction method according to the present invention is a method ofproducing a polarizing film comprising the steps of: allowing ahydrophilic polymer film to swell in an aqueous solvent, in which thefilm is conveyed by means of a guide roll so as to be impregnated in aswelling bath of the aqueous solvent; dyeing the film using a dichroicsubstance; and stretching the film. In the method, in the swelling step,at least a first guide roll is arranged in the swelling bath, and whenthe film is impregnated in and allowed to travel in the aqueous solvent,the film is brought into contact with the first guide roll afterswelling reaches saturation.

In the second production method according to the present invention, itis only required that the polymer film can be brought into contact withthe first guide roll after swelling reaches saturation. There is noparticular limitation on a required length of time (c) between the timewhen an arbitrary point on the film is brought into contact with theaqueous solvent and the time when the point is brought into contact withthe first guide roll. It is preferable that the required length of time(c) is, for example, 25 to 180 seconds for the following reason. Thatis, generally, swelling of a polymer film occurs abruptly within 15 to25 seconds as described above, and thus in the case where the requiredlength of time (c) is not shorter than 25 seconds, before the polymerfilm is brought into contact with the first guide roll, swelling of thepolymer film reaches saturation, so that the formation of wrinkles issuppressed. On the other hand, in the case where the required length oftime (c) is not longer than 180 seconds, the occurrence of slack in thepolymer film further is prevented, thereby allowing the film to beconveyed more stably. Consequently, in a polarizing film to be produced,a variation in retardation and a variation in the content of a dichroicsubstance further can be suppressed. The required length of time (c) isin the range of, preferably 30 seconds to 160 seconds, and morepreferably 40 seconds to 140 seconds. In the second production method,when the polymer film is bought into contact with the first guide roll,it is not necessarily required that swelling has reached a saturationstate as long as the swelling has already occurred abruptly.

Furthermore, similarly to the required lengths of time (a) and (b), therequired length of time (c) can be determined appropriately alsoaccording to the temperature for a swelling bath. It is particularlypreferable that the required length of time (c) is in the range of 40 to140 seconds when the temperature for the swelling bath is 40° C. to 50°C., in the range of 45 to 140 seconds when the temperature is 30° C. tolower than 40° C., and in the range of 50 to 140 seconds when thetemperature is 15° C. to lower than 30° C.

FIG. 2 is a diagrammatic view showing an example of a swelling step inthe second production method according to the present invention. Asshown in the figure, two guide rolls 41 and 42 are arranged externallyto a swelling bath 32, and one guide roll (first guide roll) 45 isarranged inside the swelling bath 32. The swelling bath 32 is filledwith an aqueous solvent 33. The guide rolls are arranged in order towardthe traveling direction of a polymer film (direction indicated by anarrow in the figure). When a polymer film 31 is conveyed by means of theguide rolls, the length between a part of the polymer film 31 that isbrought into contact with the aqueous solvent 33 and a part of thepolymer film 31 that is brought into contact with the first guide roll45 is defined as a length [c], and the time required for an arbitrarypoint on the polymer film to travel the length c is defined as arequired length of time (c). There is no particular limitation on thenumber of guide rolls to be arranged, and an additional guide rollfurther may be arranged inside or externally to a swelling bath asrequired.

In the case of using the above-mentioned swelling bath, firstly, thepolymer film 31 is conveyed by means of the guide rolls from the outsideof the swelling bath 32 (the left side in the figure) into the swellingbath so as to be impregnated in the aqueous solvent 33. Then, thepolymer film 31 is allowed to swell while traveling, and within a timeup to when the polymer film 31 reaches the first guide roll 45, thepolymer film 31 is allowed to swell to a saturation state. As for therequired length of time (c), reference should be made to the abovedescription.

The length [c] a between a part of the polymer film that is brought intocontact with the aqueous solvent in the swelling bath 32 and a part ofthe polymer film that is brought into contact with the first guide rollis not particularly limited, and is in the range of, for example, 150 to36,000 mm. Further, the speed at which the film is conveyed is, forexample, 6 to 200 mm/sec.

Next, the description is directed to an example of a sequence ofproduction steps in the first and second production methods according tothe present invention. Specifically, under the above-describedconditions, a hydrophilic polymer film is allowed to swell and is dyedusing a dichroic substance in a dyebath. The hydrophilic polymer filmfurther is stretched in a crosslinking bath, washed with water anddried, and thus a polarizing film (polarizer) is obtained.

(1) Hydrophilic Polymer Film

There is no particular limitation on the hydrophilic polymer film, andconventionally known hydrophilic polymer films can be used. Examples ofthe hydrophilic polymer film include a PVA-based film, a partiallyformalized PVA-based film, a polyethylene terephthalate (PET)-basedfilm, a film based on ethylene-vinyl acetate copolymer, andpartially-saponified films thereof. Further, alternatively, polyenealigned films of dehydrated PVA, dehydrochlorinated polyvinyl chlorideand the like, stretch-aligned polyvinylene-based films and the like alsocan be used. Among these, a PVA-based polymer film is preferable, as ithas an excellent dye-affinity provided by iodine as the above-mentioneddichroic substance. Hereinafter, the length of a polymer film in astretching direction is referred to as a “length” and the length thereofin a direction perpendicular to the stretching direction is referred toas a “width”.

Although not particularly limited, an average degree of polymerizationof the PVA film is, preferably in the range of 100 to 5,000, and morepreferably 1,000 to 4,000 in light of the water solubility of the film.Further, a saponification degree is, for example, preferably not lowerthan 75 mol %, and more preferably 98 to 100 mol %.

There is no particular limitation on the thickness of the polymer film,and the thickness is, for example, not more than 110 μm, preferably inthe range of 38 to 110 μm, more preferably 50 to 100 μm, andparticularly preferably 60 to 80 μm for the following reason. That is,with the thickness being not more than 110 μm, in the case where apolarizer as a finished product is mounted in an image display, thecolor change of a display panel can be suppressed sufficiently, and withthe thickness being in the range of 60 to 80 μm, a stretching treatmentfurther can be facilitated.

Preferably, in order to suppress, for example, a variation inretardation and a variation in the content of a dichroic substance in apolarizing film to be produced, for example, the polymer film contains aplastic material. There is no particular limitation on the content of aplastic material in the polymer film as long as it allows the effects ofthe present invention to be attained. It is preferable that with respectto a total amount (100% by mass) of the film, the plastic material iscontained in an amount of, for example, 1 to 17% by mass. With thecontent of the plastic material being in the above-mentioned range,sufficient handling ease of a polymer film can be obtained, theoccurrence of rupture further can be prevented, and an influence on theformation of the film also can be avoided sufficiently.

There is no particular limitation on the plastic material as long as itcan plasticize the polymer film, and conventionally known plasticmaterials can be used. Specifically, it is preferable to use awater-soluble plastic material, and examples thereof include glycolssuch as ethylene glycol, diethylene glycol, propylene glycol, alow-molecular-weight polyethylene glycol (Mw: 200 to 400) and the like;glycerin derivatives such as glycerin, diglycerin, triglycerin and thelike. Among these, glycerin derivatives are preferable because of theirstrong interaction with PVA and high compatibility, and glycerin isparticularly preferable. In the case where a PVA film is used as thepolymer film and glycerin is used as the water-soluble plastic materialas described above, the content of the glycerin with respect to thetotal amount (100% by mass) of the film is, preferably 3 to 16% by mass,and more preferably in the range of 5 to 15% by mass.

Preferably, the polymer film is formed of, for example a film thatallows uneven swelling to be prevented from occurring in a subsequentstep that is a swelling step, namely a film in which a variation inthickness due to swelling hardly occurs for the following reason. Thatis, by the use of such a film, in a polarizer to be produced, variationsin retardation, the content of a dichroic substance, transmittance andthe like further can be reduced. Thus, it is preferable to use a polymerfilm in which, for example, a variation in crystallinity, a variation inthickness, a variation in moisture percentage are prevented. Further, italso is preferable to use a polymer film in which a variation in thecontent of glycerin is prevented. Even in a film having a variation inthickness, since the degree of swelling is greater in a relatively thinpart and smaller in a relatively thick part, by sufficient swelling, italso is possible to reduce the problem of a variation in thickness.

(2) Swelling Treatment

The polymer film is subjected to a swelling treatment in which thepolymer film is impregnated in a swelling bath, and allowed to travel inthe swelling bath so as to satisfy the above-mentioned conditions.Preferably, in this swelling step, for example, while being allowed toswell, the polymer film is subjected to a stretching treatment for thefollowing reason. That is, by the stretching treatment, swelling furtherprogresses, and even in the case where a few wrinkles are formed on aguide roll, such wrinkles can be smoothed.

Examples of an aqueous solvent for the swelling bath include aqueoussolutions for a swelling treatment containing water, acid, alkali, anelectrolyte and the like. There is no particular limitation on the typeand concentration of the acid, alkali, and electrolyte as long as theyexert no influence on a variation in retardation and a variation in thecontent of a dichroic substance in a polarizer to be produced, andconventionally known types of acid, alkali, and an electrolyte can beused. Specifically, for example, electrolytes such as potassium, sodiumand the like and glycerin are used. Particularly, in the case where aPVA film is used as the polymer film, it is preferable that glycerin iscontained.

Preferably, the temperature of the aqueous solvent in the swelling bathis, for example, 15 to 50° C. With the temperature being not lower than15° C., a treatment can be performed in a reduced time, and thusproductivity further can be improved. With the temperature being nothigher than 50° C., sufficient optical characteristics also can beobtained.

The stretch ratio of the polymer film in the swelling treatment is, forexample, with respect to the length of the polymer film before beingsubjected to the swelling treatment (hereinafter, referred to also as a“raw film”), preferably 1.5 to 4.0 times, more preferably 1.7 to 3.8times, and still more preferably 1.9 to 3.6 times for the followingreason. That is, with such a ratio, the dye-affinity of a dichroic dyein a subsequent dyeing step is improved sufficiently, and opticalcharacteristics also can be retained sufficiently. Particularly, thelower the stretch ratio, the further dyeing unevenness in the dyeingstep, which will be described later, can be reduced. With a stretchratio of not higher than 4 times, the occurrence of stripe unevennessfurther can be suppressed.

Preferably, in the swelling step, the total length of time in which thepolymer film is impregnated in the swelling bath is not less than 100seconds for the following reason. That is, with the length of time beingnot less than 100 seconds, swelling reaches or almost reaches asaturation state, and thus for example, the stretch ratio can be reducedto about 1.1 to 1.5 times, thereby allowing dyeing unevenness to bereduced further. Meanwhile, even in the case where the total length oftime, for the impregnation is less than 100 seconds, by theabove-described stretching treatment, dyeing unevenness can be reduced.

(3) Dyeing Treatment

The polymer film is pulled out of the swelling bath, impregnated in, forexample, a dyebath containing a dichroic substance, and furtherstretched uniaxially in the dyebath. That is, the polymer film isimpregnated for adsorbing the dichroic substance and stretched forallowing the dichroic substance to be aligned in one direction.

Conventionally known substances can be used for the dichroic substance.The examples include iodine and organic dyestuffs. Preferably, in thecase of using the organic dyestuffs, at least two of the organicdyestuffs are used in combination for neutralization of the visiblelight region.

As the solution for the dyebath, an aqueous solution prepared bydissolving the dichroic substance in a solvent can be used. For example,water can be used for the solvent, and an organic solvent compatiblewith water further may be added. The concentration of the dichroicsubstance in the solution is not particularly limited, and generally isin the range of 0.1 to 10.0 parts by mass with respect to 100 parts bymass of a solvent (for example, water). The solution further may containpotassium iodide or the like as an auxiliary.

There is no particular limitation on conditions under which the polymerfilm is impregnated in the dyebath, and as the conditions, thetemperature for the dyebath is, for example, in the range of 20 to 70°C., and the length of time for the impregnation is, for example, in therange of 5 to 20 minutes. Further, preferably, the stretch ratio in thedyeing treatment is, for example, in the range of 2 to 4 times withrespect to the length of the polymer film (raw film) before beingimpregnated.

(4) Crosslinking Treatment

The polymer film is pulled out of the dyebath, impregnated in acrosslinking bath containing a crosslinking agent, and further stretchedin the crosslinking bath. The crosslinking treatment is performed toretain the running stability.

The crosslinking agent can be selected from conventionally knownsubstances including boron compounds such as boric acid, borax, glyoxal,and glutaraldehyde. These substances may be used alone, or at least twoof these may be used in combination. As the solution for thecrosslinking bath, an aqueous solution prepared by dissolving thecrosslinking agent in a solvent can be used. The solvent can be, forexample, water, and also may further contain an organic solventcompatible with water.

The concentration of the crosslinking agent in the solution is notparticularly limited, and in general, preferably is in the range of 0.1to 10% by mass with respect to 100% by mass of the solvent (for example,water). In the case where boric acid is used as the crosslinking agent,the concentration is, for example, in the range of 1.5 to 8 wt %, andpreferably in the range of 2 to 6 wt %.

In order to provide in-plane homogeneous characteristics to a polarizer,the solution may contain an auxiliary of, for example, iodide such aspotassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminumiodide, lead iodide, copper iodide, barium iodide, calcium iodide, tiniodide, titanium iodide or the like in addition to the boric acidcompound. Among these, potassium iodide is used preferably incombination with boric acid. The content of the auxiliary in thesolution is generally in the range of 0.05 to 15% by mass.

Although not particularly limited, the temperature for the crosslinkingbath is generally in the range of 20 to 70° C., and preferably in therange of 40 to 60° C. The length of time for the impregnation of thepolymer film is not particularly limited, and generally is 1 second to15 minutes.

Preferably, the stretch ratio in this crosslinking treatment is, forexample, 5 to 7 times with respect to the length of the raw film. In thecase of stretching a polymer film, there is no particular limitation onthe stretching method, the number of times stretching is performed, andthe like. Stretching may be performed in each or either of the dyeingstep and the crosslinking step as described above. Further, stretchingalso may be performed plural times in one step.

(5) Washing and Drying Treatments

The polymer film is pulled out of the stretching bath, washed with waterand dried, and thus a polarizing film is obtained. Drying can beperformed by, for example, natural drying, air-drying, heating or thelike with no particular limitation thereto. As for drying by heating,generally, the heating is performed at a temperature of 20 to 80° C. forthe length of time in the range of 1 to 10 minutes.

There is no particular limitation on the thickness of a polarizing filmaccording to the present invention as a final product. For example, thethickness is generally in the range of 1 to 80 μm, and more preferably 2to 45 μm. For example, with the thickness being not less than 1 μm,further increased mechanical strength can be obtained. Further, with thethickness being not more than 80 μm, for example, when the polarizingfilm is mounted in a liquid crystal display, the color change of adisplay panel can be suppressed sufficiently, and a reduction inthickness can be achieved easily.

Next, a polarizing film according to the present invention is apolarizing film that is produced by the first and second productionmethods according to the present invention, and can be used as, forexample, a polarizer.

Furthermore, an optical film according to the present invention ischaracterized by including the polarizing film according to the presentinvention. The following description is directed to examples of such anoptical film.

A first example of the optical film according to the present inventioncan be, for example, a polarizing plate including the polarizing filmaccording to the present invention and a transparent protective layer,in which the transparent protective layer is disposed on at least onesurface of the polarizing film. The transparent protective layer may bedisposed only on one surface or each surface of the polarizing film. Inthe case where the transparent protective layer is laminated on eachsurface, for example, transparent protective layers of the same type ordifferent types may be used.

FIG. 4 shows a cross-sectional view of an example of the polarizingplate. As shown in the figure, a polarizing plate 10 includes apolarizing film 1 and two transparent protective layers 2, and thetransparent protective layers 2 are disposed on both surfaces of thepolarizing film 1, respectively.

The transparent protective layer 2 can be selected from conventionallyknown transparent protective films without any particular limitations.It is preferable to use a transparent protective film excellent in, forexample, transparency, mechanical strength, thermal stability, amoisture shielding property, and isotropism. Specific examples ofmaterials for the above-described transparent protective layer includecellulose-based resins such as triacetylcellulose and the like, andtransparent resins based on, for example, polyester, polycarbonate,polyamide, polyimide, polyethersulfone, polysulfone, polystyrene,acrylic substances, acetate, and polyolefin. Resins based on, forexample, the acrylic substances, urethane, acrylic urethane, epoxy, andsilicones that will be cured by heat or ultraviolet rays also can beused. Further, resins having a low photoelastic coefficient such as apolynorbornene-based resin and the like also is preferable.

Other examples include a film described in JP 2001-343529 A (WO01/37007) and JP2002-328233 A, which is formed by extruding a resincomposition containing an alternating copolymer of isobutene andN-methyl maleimide and an acrylonitrile-styrene copolymer. Theabove-described film can be produced, for example, in the followingmanner. That is, firstly, the alternating copolymer (100 parts byweight) containing 50 mol % of N-methyl maleimide and 67 parts by weightof the copolymer containing 27 wt % of acrylonitrile and 73 wt % ofstyrene are melted and mixed. A pellet of a resultant mixture issupplied to a melt-extruder having a T die so as to obtain a raw film.This film is subjected to free-end longitudinal uniaxial stretchingunder conditions of a stretching speed of 100 cm/min, a stretch ratio of1.45 times and a stretching temperature of 162° C. Under the sameconditions, the film further is subjected to free-end uniaxialstretching in a direction orthogonal to the direction of theabove-mentioned stretching, and thus a stretched film having a thicknessof 49 μm is obtained. This stretched film has the respective values ofnx=1.548028, ny=1.548005, nz=1.547970, an in-plane retardation of 1.1nm, a retardation in a thickness direction of 2.8 nm, and an absolutevalue of a photoelastic coefficient of 1.9×10⁻¹³ cm²/dye.

Moreover, for example, these transparent protective films may have asurface saponified with alkali or the like. Among such films, a TAC filmis used preferably in light of its polarization characteristics anddurability. It is more preferable to use a TAC film with a saponifiedsurface.

It is preferable that the transparent protective layer is colorless, forexample. Specifically, it is preferable that a retardation value (Rth)of the film in the thickness direction as represented by the followingequation is in the range of −90 nm to +75 nm. More preferably, it isfrom −80 nm to +60 nm, and particularly preferably in the range of −70nm to +45 nm. When the retardation value is within the range of −90 nmto +75 nm, coloring (optical coloring) of the polarizing plate, which iscaused by the protective film, can be solved sufficiently.Rth=[{(nx+ny)/2}−nz]·d

In the above equation, d denotes a thickness of the transparentprotective layer, while nx, ny and nz respectively denote refractiveindices of X-axis, Y-axis and Z-axis in the transparent protectivelayer. The X axis denotes an axial direction presenting an in-planemaximum refractive index within the transparent protective layer, theY-axis denotes an in-plane axial direction perpendicular to the X-axis,and the Z-axis denotes a thickness direction perpendicular to the X-axisand the Y-axis.

There is no particular limitation on the thickness of the transparentprotective layer, and in order to achieve, for example, a reduction inthickness of the polarizing plate, the thickness is, for example, notmore than 500 μm, preferably 1 to 300 μm, and more preferably in therange of 5 to 300 μm.

Furthermore, the transparent protective layer also may be subjected to ahard coating treatment, an antireflection treatment, treatments foranti-sticking, diffusion and anti-glaring and the like. The hard coatingtreatment aims to prevent scratches on surfaces of a polarizing plate,and is a treatment of, for example, providing a hardened coating filmthat is formed of a curable resin and has excellent hardness andsmoothness onto a surface of the transparent protective layer. Thecurable resin can be selected from ultraviolet-curable resins based onsilicone, urethane, acrylic substances, epoxy and the like. Thetreatment can be performed in a conventionally known method.

The antireflection treatment aims to prevent reflection of externallight on the surface of the polarizing plate, and can be performed byforming a conventionally known antireflection film or the like. Theanti-sticking treatment aims to prevent adjacent layers from sticking toeach other.

The anti-glare treatment aims to prevent reflection of external light ona surface of the polarizing plate from hindering visibility of lighttransmitted through the polarizing plate. The anti-glare treatment canbe performed, for example, by providing microscopic asperities on asurface of the transparent protective layer by a conventionally knownmethod. Such microscopic asperities can be provided, for example, byroughening the surface by sand-blasting or embossing, or by blendingtransparent fine particles in the above-mentioned transparent resin whenforming the transparent protective layer.

The above-described transparent fine particles can be selected fromsilica, alumina, titania, zirconia, stannic oxide, indium oxide, cadmiumoxide, antimony oxide and the like and solid solutions thereof. Theaverage diameter of the above-described transparent fine particles is,for example, in the range of 0.5 to 50 μm with no particular limitationthereto. Other than the above, for example, inorganic fine particleshaving electrical conductivity or organic fine particles comprising, forexample, crosslinked or uncrosslinked polymer particles can be used aswell. Further, in general, a blend ratio of the transparent fineparticles is, preferably in the range of 2 to 50 parts by mass, and morepreferably in the range of 5 to 25 parts by mass with respect to 100parts by mass of the above-described transparent resin, though there isno particular limitation thereto.

An anti-glare layer into which the transparent fine particles areblended can be used as the transparent protective layer itself or may beformed as, for example, a coating layer applied onto a surface of thetransparent protective layer. The anti-glare layer may function also asa diffusion layer to diffuse light transmitted through the polarizingplate in order to enlarge visual angles.

The above-described antireflection film, diffusion layer, anti-glarelayer and the like also can be provided on the polarizing plate, forexample, as a sheet of optical layers comprising these layers,separately from the transparent protective layer.

The above-described polarizer can be bonded to the transparentprotective layer by a conventionally known method without any particularlimitation thereto. In general, pressure-sensitive adhesives and otheradhesives are used, and can be selected appropriately depending on, forexample, the types of the polarizing film and the transparent protectivelayer. Specific examples thereof include adhesives andpressure-sensitive adhesives formed from PVA-based, denatured PVA-based,urethane-based polymers. In order to obtain improved durability,water-soluble crossliking agents for crosslinking vinyl alcohol-basedpolymers such as boric acid, borax, glutaraldehyde, melamine, oxalicacid, chitin, chitosan, metal salts, alcohol-based solvents and the likemaybe added in these adhesives and the like. In the case where aPVA-based film is used as the polarizer, PVA-based adhesives are usedpreferably in light of, for example, stability of an adhering treatment.The thickness of such an adhesive layer is not particularly limited, andis, for example, 1 nm to 500 nm, preferably 10 nm to 300 nm, and morepreferably 20 nm to 100 nm.

Preferably, in the case where the polarizer is bonded to the transparentprotective layer with the adhesive, for example, in order to preventpeeling from occurring due to the influence of moisture and heat and toobtain a polarizing plate excellent in transmittance and polarizationdegree, a drying treatment is performed. The temperature at which dryingis performed is not particularly limited and can be determinedappropriately according to, for example, the type of an adhesive or apressure-sensitive adhesive that is used. In the case where the adhesiveis the above-mentioned PVA-based, denatured PVA-based, urethane-basedwater-soluble adhesive or the like, for example, drying is performed ata temperature of, preferably 60 to 70° C., and more preferably 60 to 75°C. for, preferably about 1 to 10 minutes.

Furthermore, preferably, the polarizing plate according to the presentinvention further includes a pressure-sensitive adhesive layer providedin its outermost layer in order to facilitate lamination onto, forexample, a liquid crystal cell or the like. FIG. 5 shows across-sectional view of a polarizing plate including apressure-sensitive adhesive layer as described above. As shown in thefigure, a polarizing plate 20 includes the polarizing plate 10 shown inFIG. 4 and a pressure-sensitive adhesive layer 3, and thepressure-sensitive adhesive layer 3 further is disposed on a surface ofone of the transparent protective layers 2 of the polarizing plate 10.

The pressure-sensitive adhesive layer can be formed on the surface ofthe transparent protective layer, for example, in the following manners.That is, a solution or melt of a pressure-sensitive adhesive is applieddirectly on a predetermined surface of the transparent protective layerby an expanding method such as flow-expanding, coating or the like.Alternatively, a pressure-sensitive adhesive layer is formed similarlyon a separator, which will be described later, and transferred onto apredetermined surface of the transparent protective layer. Such apressure-sensitive adhesive layer may be formed on either surface of apolarizing plate as shown in FIG. 5 with no limitation thereto, and alsomay be disposed on each surface thereof as required.

The pressure sensitive adhesive layer can be formed by appropriatelyusing any of conventionally known pressure-sensitive adhesives based on,for example, acrylic substances, silicone, polyester, polyurethane,polyether, rubber and the like. Particularly, pressure-sensitiveadhesives having a low moisture absorption coefficient and excellentheat resistance are used preferably from the aspects of prevention offoaming or peeling caused by moisture absorption, prevention ofdeterioration in optical characteristics and warping of a liquid crystalcell caused by a difference in thermal expansion coefficients, andformation of a liquid crystal display with high quality and excellentdurability. Examples of such a pressure-sensitive adhesive includepressure-sensitive adhesives based on acrylic substances, silicone,acrylic-silicone, polyester, heat-resistant rubber and the like.Further, for example, a pressure-sensitive adhesive layer that containsfine particles and exhibits a light diffusion property also may be used.

Furthermore, in the case where a surface of a pressure-sensitiveadhesive layer provided on the polarizing plate is exposed, it ispreferable to cover the surface with a separator for, for example, theprevention of contamination until the pressure-sensitive adhesive layeris put into use. The separator can be formed of, for example, a suitablethin film such as the above-mentioned transparent protective film or thelike that is provided with a release coat such as a coat of asilicone-based release agent, a long-chain alkyl-based release agent, afluorine-based release agent or molybdenum sulfide, as required.

The thickness of the pressure-sensitive adhesive layer is notparticularly limited, and is, for example, preferably 5 to 35 μm, morepreferably 10 to 25 μm, and particularly preferably 15 to 25 μm for thefollowing reason. That is, with the thickness being set to be in theabove-mentioned ranges, for example, even when a polarizing plate ischanged in size, a stress caused at that time also can be relieved.

Furthermore, the polarizing plate according to the present invention canbe used to form a liquid crystal cell, a liquid crystal display or thelike. In this case, the polarizing plate may be prepared, for example,in the following manners. That is, a laminate of the polarizer, atransparent protective layer and the like is subjected to cutting(chip-cutting) so as to correspond to the size of a liquid crystal cellor the like. Alternatively, the polarizer is subjected to cuttingbeforehand, and then the transparent protective layer is bonded thereto.

Next, a second example of the optical film according to the presentinvention is a laminate including the polarizer according to the presentinvention or the polarizing plate of the first example and at least oneof a polarization converting element and a retardation film.

There is no particular limitation on the polarization convertingelement. Examples thereof include an anisotropic reflective polarizationelement and an anisotropic scattering polarization element that are usedcommonly to form liquid crystal displays. For example, one or more ofthese polarization converting elements may be laminated. Further, in thecase of laminating two or more layers, the layers may be of the sametype or different types.

Among the polarization converting elements, the anisotropic reflectivepolarization element is, for example, a composite of a cholestericliquid crystal layer and a retardation plate, and it is preferable thatthe retardation plate has a retardation value that is 0.2 to 0.3 times awavelength within a reflection band of the anisotropic reflectivepolarizer. It is more preferable that the retardation value is 0.25times the wavelength. As the cholesteric liquid crystal layer,particularly, for example, an alignment film of a cholesteric liquidcrystal polymer or an alignment liquid crystal layer fixed onto a filmsubstrate, which reflects either clockwise or counterclockwisecircularly polarized light while transmitting other light is usedpreferably. As such an anisotropic reflective polarization element, forexample, trade name PCF series produced by Nitto Denko Corporation, canbe used. The above-mentioned wavelength is arbitrary as long as thewavelength is within the reflection band of the anisotropic reflectivepolarizer. Further, the cholesteric liquid crystal layer also may be amultilayer thin film of a dielectric or a multilayer laminate of thinfilms varying in refractive index anisotropy, which transmits linearlypolarized light having a predetermined polarization axis whilereflecting other light. As such an anisotropic reflective polarizationelement, for example, trade name DBEF series produced by 3M Co., can beused.

Furthermore, as the anisotropic reflective polarization element, areflective grid polarizer is used preferably, and specific examplesthereof include trade name MicroWires produced by Moxtek, Inc.

Meanwhile, as the anisotropic scattering polarization element, forexample, trade name DRPF produced by 3M Co. can be used.

Next, a third example of the optical film according to the presentinvention can be, for example, any of various types of polarizing platesthat are laminates including, as well as various optical layers, thepolarizer according to the present invention, the polarizing plate ofthe first example, or the laminate of the second example. Though thereis no particular limitation on the optical layers, the examples includeoptical layers used for forming liquid crystal displays and the like,i.e., a reflector, a semitransparent reflector, a retardation plate suchas, for example, a λ plate like a half wavelength plate and a quarterwavelength plate or the like, a visual angle compensating film, and abrightness enhancement film. These optical layers may be used alone ortwo or more types of these layers may be used in combination. Aspolarizing plates including such optical layers, particularly preferableare a reflective polarizing plate, a semitransparent reflectivepolarizing plate, an elliptically polarizing plate, a circularlypolarizing plate, a polarizing plate on which a visual anglecompensating film is laminated, and a polarizing plate on which abrightness enhancement film is laminated.

The respective polarizing plates will be described below.

First, an example of a reflective polarizing plate or a semitransparentreflective polarizing plate according to the present invention will bedescribed. The reflective polarizing plate is formed of, for example,the polarizing plate described in the first example on which a reflectorfurther is laminated. The semitransparent reflective polarizing plate isformed of the polarizing plate on which a semitransparent reflector islaminated.

In general, the reflective polarizing plate is arranged on the backsideof a liquid crystal cell in order to make a liquid crystal display(reflective liquid crystal display) to reflect incident light from aviewing side (display side). The reflective polarizing plate has someadvantages, for example, that assembling of light sources such as abacklight can be omitted, and that the liquid crystal display can bethinned further.

The reflective polarizing plate can be formed by any conventionallyknown method such as forming a reflector of metal or the like on onesurface of the polarizing plate that has been subjected to theabove-described heating treatment. Specifically, for example, atransparent protective layer of the polarizing plate is prepared bymatting one surface (exposed surface) if required. On this surface, afoil comprising a reflective metal such as aluminum or a deposition filmis applied as a reflector to form a reflective polarizing plate.

Another example of the reflective polarizing plate is formed in thefollowing manner. That is, as described above, fine particles arecontained in any of various types of transparent resins to form atransparent protective layer with a surface on which microscopicasperities are provided, and a reflector corresponding the microscopicasperities is formed on the transparent protective layer. The reflectorhaving a microscopic asperity surface has an advantage of, for example,diffusing incident light by irregular reflection so that directivity andglare can be prevented and unevenness of color tones can be suppressed.This reflector can be formed as the metal foil or a metal depositionfilm directly on a microscopic asperity surface of the transparentprotective layer by any of conventionally known methods includingdeposition such as vacuum deposition, and plating such as ion platingand sputtering.

As mentioned above, the reflector can be formed directly on atransparent protective layer of a polarizing plate. Alternatively, asthe reflector, for example, a reflecting sheet formed by providing areflecting layer on a proper film similar to the transparent protectivefilm may be used. In general, the reflecting layer in the reflector ismade of a metal, and thus it is preferable to use the reflecting layerin a state where a reflecting surface thereof is coated with the film, apolarizing plate or the like from the aspects of, for example,preventing a decrease in reflection rate due to oxidation, therebymaintaining an initial reflection rate for a long period, andeliminating the need of forming an additional transparent protectivelayer.

The semitransparent polarizing plate is provided by replacing thereflector in the above-described reflective polarizing plate by asemitransparent reflector. The semitransparent reflector is exemplifiedby a half mirror that reflects and transmits light at a reflectinglayer.

In general, the semitransparent polarizing plate is arranged on thebackside of a liquid crystal cell. In a liquid crystal display or thelike comprising the semitransparent polarizing plate, incident lightfrom a viewing side (display side) is reflected to display an image whenthe liquid crystal display or the like is used in a relatively brightatmosphere, while in a relatively dark atmosphere, an image is displayedby using a built-in light source such as a backlight in the backside ofthe semitransparent polarizing plate. In other words, thesemitransparent polarizing plate can be used effectively to form aliquid crystal display or the like that can save energy for a lightsource such as a backlight under a bright atmosphere, while using thebuilt-in light source under a relatively dark atmosphere.

Next, an example of an elliptically polarizing plate or a circularlypolarizing plate according to the present invention will be described.Each of these polarizing plates is formed of, for example, theabove-described polarizing plate of the first example on which aretardation plate or a λ plate further is laminated.

The elliptically polarizing plate is effective, for example, incompensating (preventing) colors (blue or yellow) generated due tobirefringence in a liquid crystal layer of a super twist nematic (STN)liquid crystal display so as to provide black-and-white display free ofsuch colors. An elliptically polarizing plate with a controlledthree-dimensional refractive index is further preferable since it cancompensate (prevent) colors that will be observed when a screen of theliquid crystal display is viewed from an oblique direction. Thecircularly polarizing plate is effective, for example, in adjustingcolor tones of an image of a reflective liquid crystal display providingcolor image display, and serves to prevent reflection as well.

The retardation plate is used for converting linearly polarized lightinto either elliptically polarized light or circularly polarized light,converting either elliptically polarized light or circularly polarizedlight into linearly polarized light, or modifying a polarizationdirection of linearly polarized light. Particularly, for example, aretardation plate called a quarter wavelength plate (referred to also asa λ/4 plate) is used for converting linearly polarized light into eitherelliptically polarized light or circularly polarized light, and forconverting either elliptically polarized light or circularly polarizedlight into linearly polarized light. A half wavelength plate (referredto also as a λ/2 plate) is used in general for modifying a polarizationdirection of linearly polarized light.

Examples of the retardation plate include birefringent films, alignmentfilms of liquid crystal polymers, and laminates of alignment layers ofliquid crystal polymers supported by films. The birefringent films canbe prepared by stretching polymer films such as films of polycarbonate,PVA, polystyrene, polymethyl methacrylate, polyolefins includingpolypropylene, polyalylate, polyamide, polynorbornene, and the like.

The retardation plate may have a retardation suitable for intended usessuch as compensation of a visual angle for, for example, enlarging avisual angle and compensation of coloring caused by birefringence in aliquid crystal layer or plates having varying wavelengths such as thehalf wavelength plate, the quarter wavelength plate and the like.Alternatively, the retardation plate may be an inclined alignment filmhaving a controlled refractive index in the thickness direction. Two ormore types of retardation plates may be laminated for forming a laminatewith controlled optical characteristics such as a retardation and thelike.

The inclined alignment film is produced, for example, by bonding a heatshrinkable film to a polymer film and stretching and/or shrinking thepolymer film under an action of a shrinkage force provided by heating,or by obliquely aligning a liquid crystal polymer.

Next, the description is directed to an example of a polarizing plateformed of the polarizing plate of the first example on which a visualangle compensating film further is laminated.

The visual angle compensating film is used, for example, for widening avisual angle so that an image can be clear relatively when a screen of aliquid crystal display is viewed not in a direction perpendicular to thescreen but in a slightly oblique direction. Such a visual anglecompensating film can be, for example, a triacetylcellulose film or thelike coated with a discotic liquid crystal, or a retardation plate.While an ordinary retardation plate is, for example, a birefringentpolymer film that is stretched uniaxially in its plane direction, aretardation plate used for the visual angle compensating film is, forexample, a two-way stretched film such as a birefringent polymer filmstretched biaxially in a plane direction and an inclined alignmentpolymer film with a controlled refractive index in a thickness directionthat is stretched uniaxially in a plane direction and stretched also ina thickness direction. The inclined alignment film is prepared, forexample, by bonding a heat shrinkable film to a polymer film andstretching and/or shrinking the polymer film under an action of ashrinkage force provided by heating, or by obliquely aligning a liquidcrystal polymer. The polymer film can be formed from a material similarto the above-mentioned polymers used to form the above-describedretardation plate.

Next, the description is directed to an example of a polarizing plateformed of the polarizing plate of the first example on which abrightness enhancement film further is laminated.

Generally, this polarizing plate is arranged on a backside of a liquidcrystal cell. When natural light enters, for example, by reflection froma backlight or a backside of a liquid crystal display or the like, thebrightness enhancement film reflects linearly polarized light of apredetermined polarization axis or circularly polarized light in apredetermined direction while transmitting other light. It allowsentrance of light from a light source such as a backlight so as toobtain transmitted light in a predetermined polarization state, whilereflecting light other than light in the predetermined polarizationstate. Light that is reflected at this brightness enhancement film isreversed through a reflector or the like arranged behind the brightnessenhancement film. The reversed light that re-enters the brightnessenhancement film is transmitted partly or entirely as light in thepredetermined polarization state, so that light transmitted through thebrightness enhancement film is increased and polarized light that ishardly absorbed in a polarizing film (polarizer) is supplied. As aresult, quantity of light available for liquid crystal display or thelike can be increased to enhance brightness. When light enters throughthe polarizer from the backside of a liquid crystal cell by using abacklight or the like without using the brightness enhancement film,most light is absorbed in the polarizer but not transmitted through thepolarizer if the light has a polarization direction inconsistent withthe polarization axis of the polarizer. Depending on characteristics ofthe polarizer that is used, about 50% of light is absorbed in thepolarizer, and this decreases quantity of light available for liquidcrystal display or the like and makes the image dark. The brightnessenhancement film repeatedly prevents light having a polarizationdirection with which light is absorbed in the polarizer from enteringthe polarizer, reflects the light once on the brightness enhancementfilm, further reverses the light through a reflector or the likearranged behind the brightness enhancement film, and makes the lightre-enter the brightness enhancement film. Since the polarized light thatis reflected and reversed between them is transmitted and supplied tothe polarizer only if the light has a polarization direction with whichlight can be transmitted through the polarizer, light from a backlightor the like can be used efficiently for displaying images of a liquidcrystal display in order to provide a bright screen.

A diffusion plate may be arranged between the brightness enhancementfilm and the reflecting layer or the like. In this case, polarized lightreflected by the brightness enhancement film is directed to thereflecting layer. The diffusion plate diffuses the light beingtransmitted therethrough uniformly and at the same time, it cancels thepolarization so as to provide a depolarized state. Namely, the diffusionplate converts the light back into its original state as natural light.This depolarized light, i.e., natural light is directed to thereflecting layer or the like, reflected at the reflecting layer, andtransmitted again through the diffusion plate so as to re-enter thebrightness enhancement film. The state of natural light is recovered byrepeating this series of actions. Thereby, the diffusion plate serves,for example, to maintain brightness of the display screen and decreaseunevenness of the brightness at the same time, and thus a screen withuniform brightness can be provided. Further, the diffusion plate has adiffusion function and further can increase appropriately the repeatedreflection of the initial incident light. Conceivably, this makes itpossible to provide a display screen with uniform brightness.

Though there is no particular limitation, the brightness enhancementfilm can be selected from a multilayer thin film of a dielectric and amultilayer laminate of thin films varying in refractive index anisotropythat transmit linearly polarized light having a predeterminedpolarization axis while reflecting other light. Specifically, forexample, trade name D-BEF produced by 3M Co. can be used as thebrightness enhancement film. The brightness enhancement film also maybe, for example, a cholesteric liquid crystal layer, particularly, analignment film of a cholesteric liquid crystal polymer, or an alignmentliquid crystal layer fixed onto a film substrate that reflects eitherclockwise or counterclockwise circularly polarized light whiletransmitting other light. Examples of such a film include trade name“PCF350” produced by Nitto Denko Corporation and trade name Transmaxproduced by Merck and Co., Inc.

Therefore, for a brightness enhancement film to transmit linearlypolarized light having a predetermined polarization axis, for example,the transmission light enters the polarizing plate by matching thepolarization axis so that absorption loss due to the polarizing plate issuppressed and the light can be transmitted efficiently. For abrightness enhancement film to transmit circularly polarized light,i.e., a cholesteric liquid crystal layer, preferably, the transmissioncircularly polarized light is converted into linearly polarized lightbefore entering the polarizing plate from the aspect of suppressing theabsorption loss, though the circularly polarized light can enter thepolarizer directly. Circularly polarized light can be converted intolinearly polarized light by using, for example, a quarter wavelengthplate for a retardation plate.

A retardation plate having a function as a quarter wavelength plate in awide wavelength range including a visible light region can be obtained,for example, by laminating a retardation layer functioning as a quarterwavelength plate for monochromatic light such as light having 550 nmwavelength and another retardation layer exhibiting other opticalretardation characteristics (for example, a retardation layerfunctioning as a half wavelength plate). Therefore, a retardation platearranged between a polarizing plate and a brightness enhancement filmmay comprise a single layer or at least two layers of retardationlayers. A cholesteric liquid crystal layer also can be provided bycombining layers different in the reflection wavelength and it can beconfigured by laminating two or at least three layers. As a result, theobtained retardation plate can reflect circularly polarized light in awide wavelength range including a visible light region, and this canprovide transmission circularly polarized light in a wide wavelengthrange.

Each of the above-described various types of polarizing plates of thethird example also may be, for example, an optical film made bylaminating the above-described polarizing plate and two or at leastthree additional optical layers. Specific examples thereof include areflective elliptically polarizing plate or a semitransparentelliptically polarizing plate that is prepared by combining either theabove-described reflective polarizing plate or semitransparentpolarizing plate with a retardation plate.

As described above, an optical film comprising a laminate of at leasttwo optical layers can be formed by, for example, a method of laminatinglayers separately in a certain order for producing a liquid crystaldisplay or the like. Alternatively, an optical member of laminates thathave been laminated previously also can be used advantageously since ithas excellent stability in quality and assembling operability, therebyproviding improved efficiency in producing a liquid crystal display orthe like. In the same manner as described above, any adhesion means suchas a pressure-sensitive adhesive layer or the like can be used for thelamination.

The above-described members constituting the optical film according tothe present invention, i.e. the polarizing film, the transparentprotective layer, the optical layer, the pressure-sensitive adhesivelayer and the like may have ultraviolet absorption power as a result ofan appropriate treatment with an ultraviolet absorber such as an estersalicylate compound, a benzophenone compound, a benzotriazole compound,a cyanoacrylate compound, a nickel complex salt compound or the like.

Next, a liquid crystal panel according to the present invention includesat least one of the polarizer and optical film (hereinafter, referred toalso as an “optical film”) according to the present invention, which isdisposed on at least one surface of a liquid crystal cell.

There is no particular limitation on the type of the liquid crystalcell, and conventionally known liquid crystal cells can be usedappropriately. Particularly, since the polarizer and the like accordingto the present invention are used effectively in a liquid crystaldisplay that allows polarized light to be incident on a liquid crystalcell to provide display, for example, liquid crystal cells using a TN(Twisted Nematic) liquid crystal and a STN (Super Twisted Nematic)liquid crystal are preferable. Further, alternatively, for example, aliquid crystal cell using a non-twisted liquid crystal such as of an IPS(In-Plane Switching) mode, a VA (Vertical Aligned) mode, or an OCB(Optically Compensated Birefringence) mode, a liquid crystal cell usinga guest-host liquid crystal in which the above-mentioned dichroic dye isdispersed, or a liquid crystal cell using a ferroelectric liquid crystalalso can be used. The method of driving a liquid crystal also is notparticularly limited.

An optical film such as the above-described polarizing plate or the likemay be disposed only on one surface or each surface of the liquidcrystal cell. In the case where the optical film is disposed on eachsurface of the liquid crystal cell, optical films of the same type ordifferent types may be used. Further, in the case where a polarizingplate and an optical member are provided on each side of a liquidcrystal cell, these members may be of the same type or different types,respectively.

Furthermore, one or at least two components in general use such as aprism array sheet, a lens array sheet, a light diffusion plate and thelike further may be arranged at suitable positions, respectively.

FIGS. 6 to 8 show examples of a liquid crystal panel in which theoptical film according to the present invention is disposed. In each ofthese figures, a state of lamination of a liquid crystal cell and theoptical film is shown in cross section, and constituents aredistinguished by hatching. Further, in the figures, like referencenumerals indicate like members. The liquid crystal panel according tothe present invention is not limited to these examples.

A liquid crystal panel shown in FIG. 6 includes a liquid crystal cell 12and polarizing plates 11, and the polarizing plates 11 are provided onboth surfaces of the liquid crystal cell 12, respectively. There is noparticular limitation on the structure of the liquid crystal cell (notshown), and the liquid crystal cell generally has a structure in which aliquid crystal is held between an array substrate and a filtersubstrate.

Furthermore, a liquid crystal panel shown in FIG. 7 includes a liquidcrystal cell 12, polarizing plates 11 and retardation plates 13, and thepolarizing plates 11 are laminated on both surfaces of the liquidcrystal cell 12 through the retardation plates 13, respectively. Theretardation plate 13 and the polarizing plate 11 also may be usedintegrally as the optical film according to the present invention anddisposed on each surface of the liquid crystal cell 12.

A liquid crystal panel shown in FIG. 8(A) includes a liquid crystal cell12, polarizing plates 11 and a polarization converting element 14. Thepolarizing plates 11 are laminated respectively on both surfaces of theliquid crystal cell 12, and the polarization converting element 14further is laminated on one surface of one of the polarizing plates. Thepolarization converting element 14 can selected from the above-describedelements, and examples thereof include a composite of a quarterwavelength plate 15 and a cholesteric liquid crystal 16 shown in FIG.8(B) and an anisotropic multiple thin-film reflective polarizationelement 17 shown in FIG. 8(C). The polarizing plate 11 and thepolarization converting element 14 also may be used integrally as theoptical film according to the present invention and disposed on onesurface of the liquid crystal cell 12.

Next, a liquid crystal display according to the present invention is aliquid crystal display including a liquid crystal panel, in which theliquid crystal panel is the liquid crystal panel according to thepresent invention.

The liquid crystal display further may include a light source. The lightsource is not particularly limited, and preferably is, for example, aflat light source that emits polarized light so as to allow light energyto be used effectively.

In the liquid crystal display according to the present invention, forexample, a diffusion plate, an anti-glare layer, an antireflection film,a protective layer/plate further can be arranged on an optical film(polarizing plate) at a viewing side. Alternatively, for example, aretardation plate for compensation can be arranged appropriately betweena liquid crystal cell and a polarizing plate in a liquid crystal panel.

Next, an electroluminescence (EL) display according to the presentinvention is a display including at least one of the polarizer accordingto the present invention and the optical film according to the presentinvention. This EL display may be either of an organic EL display and aninorganic EL display.

Recently, for EL displays, for example, use of an optical film such as apolarizer, a polarizing plate or the like together with a λ/4 plate issuggested for preventing reflection from an electrode in a black state.The polarizer and optical film according to the present invention isuseful particularly when any of linearly polarized light, circularlypolarized light or elliptically polarized light is emitted from an ELlayer, or when obliquely emitted light is polarized partially even ifnatural light is emitted in the front direction.

The following description is about a typical organic EL display. Ingeneral, the organic EL display has a luminant (organic EL ruminant)that is prepared by laminating a transparent electrode, an organicluminant layer and a metal electrode in this order on a transparentsubstrate. Here, the organic luminant layer is a laminate of variousorganic thin films. Known examples thereof include a laminate of a holeinjection layer made of a triphenylamine derivative or the like and aluminant layer made of a phosphorous organic solid such as anthracene orthe like; a laminate of the luminant layer and an electron injectionlayer made of a perylene derivative or the like; and a laminate of thehole injection layer, the luminant layer and the electron injectionlayer.

The organic EL display emits light on the principle of a system in whicha voltage is applied to the anode and the cathode so as to inject holesand electrons into the organic luminant layer, energy generated by there-bonding of these holes and electrons excites the phosphor, and theexcited phosphor emits light when it returns to the basis state. There-bonding mechanism of the holes and electrons is similar to that of anordinary diode. Current and the light emitting intensity exhibit aconsiderable nonlinearity accompanied with rectification with respect tothe applied voltage.

It is required for the organic EL display that at least one of theelectrodes be transparent so as to obtain luminescence at the organicluminant layer. In general, a transparent electrode of a transparentconductive material such as indium tin oxide (ITO) or the like is usedfor the anode. Use of substances having small work function for thecathode is effective for facilitating the electron injection and therebyraising luminous efficiency, and in general, metal electrodes such as ofMg—Ag, Al—Li and the like may be used.

In an organic EL display configured as described above, it is preferablethat the organic luminant layer is made of a film that is as extremelythin as about 10 nm. This allows the organic luminant layer to transmitsubstantially whole light as the transparent electrode does. As aresult, when the layer does not illuminate, light entering from thesurface of the transparent substrate is transmitted through thetransparent electrode and the organic ruminant layer to be reflected atthe metal layer, and it comes out again to the surface side of thetransparent substrate. Thereby, the display surface of the organic ELdisplay looks like a mirror when viewed from exterior.

The organic EL display according to the present invention includes, forexample, the organic EL ruminant formed by providing a transparentelectrode on the surface side of the organic ruminant layer and a metalelectrode on the backside of the organic ruminant layer, and preferably,the polarizing film (for example, a polarizing plate) according to thepresent invention is arranged on the surface of the transparentelectrode. More preferably, a λ/4 plate is arranged between thepolarizing plate and an EL device. By arranging the optical filmaccording to the present invention, the organic EL display has an effectof suppressing external reflection and improving visibility. It is alsopreferable that a retardation plate further is arranged between thetransparent electrode and the optical film.

The retardation plate and the optical film (for example, the polarizingplate or the like) function to polarize light which enters from outsideand is reflected by the metal electrode, and thus the polarization hasan effect that the mirror of the metal electrode cannot be viewed fromexterior. Particularly, the mirror of the metal electrode can be blockedcompletely by forming the retardation plate with a quarter wavelengthplate and adjusting an angle formed by the polarization direction of theretardation plate and the polarizing plate to be π/4. That is, thepolarizing plate transmits only the linearly polarized light constituentamong the external light entering the organic EL display. In general,the linearly polarized light is converted into elliptically polarizedlight by the retardation plate. When the retardation plate is a quarterwavelength plate and when the angle of the polarization directionprovided by the polarizing plate and the retardation plate is π/4, thelight turns into circularly polarized light.

This circularly polarized light is transmitted through the transparentsubstrate, the transparent electrode, and the organic thin films. Afterbeing reflected by the metal electrode, the light is transmitted againthrough the organic thin films, the transparent electrode and thetransparent substrate, and turns into linearly polarized light at theretardation plate. Moreover, since the linearly polarized light crossesthe polarization direction of the polarizing plate at a right angle, itcannot pass through the polarizing plate. As a result, the mirror of themetal electrode can be blocked completely as described above.

Furthermore, an in-house production method of a liquid crystal displayand an EL display according to the present invention is a productionmethod including a step in which at least one of the polarizer accordingto the present invention and the optical film according to the presentinvention, in each of which a surface protective film is provided on adisplay surface side, and a pressure-sensitive adhesive layer and arelease layer are provided on the other surface, is attached to thedisplay immediately after being subjected to chip-cutting.

In the in-house production method for producing various displays inwhich the polarizer or the optical film is cut and attached to a liquidcrystal cell or the like in a seamless manner as described above, forexample, measurement should be performed instantly in order to detect adefective area, and thus it is required to determine the need formarkings by establishing a boundary sample or performing in-linemeasurement. According to the production method of the presentinvention, various displays can be produced in the following manner.That is, with respect to the polarizer or optical film according to thepresent invention, markings are provided on portions that do not satisfythe conditions, and immediately after performing punching, the polarizeror the optical film is attached to a liquid crystal panel or an ELdisplay. As described above, with respect to a polarizer or an opticalfilm, a sequence of steps of punching, screening and attaching can beperformed in a seamless manner, and thus inspection can be performed ina shorter time, thereby also allowing production to be simplified andless costly. Generally, in-house production refers to a total line ofproduction in which with respect to a rolled raw film of a polarizingplate, punching, inspection and attaching to a LCD are performed.

EXAMPLES

Next, the present invention will be described further by way of thefollowing examples and comparative examples. However, the presentinvention is not limited only to these examples. Unless otherwisespecified, “%” represents “% by mass”.

Example 1

As shown in FIG. 1, two guide rolls (flat rolls) were arranged in aswelling bath, and pure water as a swelling solvent was put therein andkept at 25° C. beforehand. Araw PVA film (trade name VF-PS#7500;produced by Kuraray Co., Ltd.) having a thickness of 75 μm was conveyedby means of the guide rolls into the swelling bath so as to be swollentherein, and further was stretched to a length 2.5 times the length ofthe raw film. A length of time (a) between the time when the film wasbrought into contact with the solvent in the swelling bath and the timewhen the film was brought into contact with a first guide roll byconveyance was set to be 3.5 seconds, and a length of time (b) betweenthe time when the film was brought into contact with the first guideroll and the time when the film was brought into contact with a secondguide roll was set to be 60 seconds. Further, an arbitrary point on thefilm was impregnated in the swelling bath for 92 seconds in total.

This film was impregnated in a mixed solution of 0.04% iodine and 0.4%potassium iodide (hereinafter, referred to as a dyebath), and dyedtherein while being stretched to a length 3 times the length of the rawfilm. The film further was impregnated in an aqueous solution of 3.5%boric acid (stretching bath) and stretched to a length 6 times thelength of the raw film, and thus a polarizing film (having a thicknessof 27 μm) was formed. Further, a TAC film (trade name TD-80U; producedby Fuji Photo Film Co., Ltd.) having a thickness of 80 μm wassaponified, and a resultant film was attached to each surface of theabove-described polarizing film using an aqueous solution of 1% PVA anddried, and thus a polarizing plate was formed.

Example 2

A polarizing film and a polarizing plate were formed in the same manneras in Example 1. However, in this example, in a swelling treatment, alength of time (a) between the time when a film was brought into contactwith a solvent in a swelling bath and the time when the film was broughtinto contact with a first guide roll by conveyance was set to be 2seconds, and a length of time (b) between the time when the film wasbrought into contact with the first guide roll and the time when thefilm was brought into contact with a second guide roll was set to be 35seconds. An arbitrary point on the film was impregnated in the swellingbath for 63 seconds in total.

Example 3

A polarizing film and a polarizing plate were formed in the same manneras in Example 1. However, in this example, in a swelling treatment, alength of time (a) between the time when a film was brought into contactwith a solvent in a swelling bath and the time when the film was broughtinto contact with a first guide roll by conveyance was set to be 11seconds, and a length of time (b) between the time when the film wasbrought into contact with the first guide roll and the time when thefilm was brought into contact with a second guide roll was set to be 110seconds. An arbitrary point on the film was impregnated in the swellingbath for 130 seconds in total.

Example 4

A polarizing film and a polarizing plate were formed in the same manneras in Example 1. However, in this example, as shown in FIG. 2, one guideroll was arranged in a swelling bath, and a length of time (c) betweenthe time when a film was brought into contact with a solvent in theswelling bath and the time when the film was brought into contact with afirst guide roll by conveyance was set to be 70 seconds. An arbitrarypoint on the film was impregnated in the swelling bath for 75 seconds intotal.

Example 5

As shown in FIG. 1, two guide rolls were arranged in a swelling bath,and water as a swelling solvent was put therein and kept at 32° C.beforehand. A raw PVA film (trade name OPL-M; produced by The NipponSynthetic Chemical Industry Co., Ltd.) having a thickness of 75 μm wasconveyed by means of the guide rolls into the swelling bath so as to beswollen therein, and further was stretched to a length 1.9 times thelength of the raw film. A length of time (a) between the time when thefilm was brought into contact with the solvent in the swelling bath andthe time when the film was brought into contact with a first guide rollby conveyance was set to be 5 seconds, a the length of time (b) betweenthe time when the film was brought into contact with the first guideroll and the time when the film was brought into contact with a secondguide roll was set to be 77 seconds. An arbitrary point on the film wasimpregnated in the swelling bath for 121 seconds in total.

This film was impregnated in a mixed solution of 0.04% iodine and 0.4%potassium iodide (dyebath), and dyed therein while being stretched to alength 2.8 times the length of the raw film. The film further wasimpregnated in an aqueous solution of 3.5% boric acid (stretching bath)and stretched to a length 6 times the length of the raw film, and thus apolarizing film (having a thickness of 30 μm) was formed. Further, a TACfilm that is the same as described above was saponified, and a resultantfilm is attached to each surface of the polarizing film using an aqueoussolution of 1% PVA and dried, and thus a polarizing plate was formed.

Example 6

A polarizing film and a polarizing plate were formed in the same manneras in Example 1. However, in this example, a PVA film that is the sameas used for Example 5 was used, and spiral rolls were used as the guiderolls. Further, a length of time (a) between the time when the film wasbrought into contact with a solvent in a swelling bath and the time whenthe film was brought into contact with a first guide roll was set to be11 seconds, and a length of time (b) between the time when the film wasbrought into contact with the first guide roll and the time when thefilm was brought into contact with a second guide roll was set to be 110seconds. A groove (indentation) of the spiral rolls had a width of 1 cmand a depth of 1 cm. An arbitrary point on the film was impregnated inthe swelling bath for 128 seconds in total.

Example 7

A polarizing film and a polarizing plate were formed in the same manneras in Example 1. However, in this example, a PVA film that is the sameas used for Example 5 was used, and crown rolls were used as the guiderolls. Further, with respect to the length of a raw film, a stretchratio of stretching in a swelling bath was set to be 2.1 times, and astretch ratio of stretching in a dyebath was set to be 2.9 times.Further, a length of time (a) between the time when the film was broughtinto contact with a solvent in the swelling bath and the time when thefilm was brought into contact with a first guide roll by conveyance wasset to be 2 seconds, and a length of time (b) between the time when thefilm was brought into contact with the first guide roll and the timewhen the film was brought into contact with a second guide roll was setto be 35 seconds. An arbitrary point on the film was impregnated in theswelling bath for 63 seconds in total.

Example 8

A polarizing film and a polarizing plate were formed in the same manneras in Example 1. However, in this example, a PVA film that is the sameas used for Example 5 was used, and the temperature of a swelling bathwas set to be 42° C. Further, in a swelling treatment, a length of time(a) between the time when the film was brought into contact with asolvent in a swelling bath and the time when the film was brought intocontact with a first guide roll by conveyance was set to be 6 seconds,and a length of time (b) between the time when the film was brought intocontact with the first guide roll and the time when the film was broughtinto contact with a second guide roll was set to be 60 seconds. Anarbitrary point on the film was impregnated in the swelling bath for 95seconds in total

Example 9

A polarizing film and a polarizing plate were formed in the same manneras in Example 4. However, in this example, as shown in FIG. 2, one guideroll (crown roll) was arranged in a swelling bath, and a PVA film thatis the same as used for Example 5 was used. Further, a length of time(c) between the time when the film was brought into contact with asolvent in the swelling bath and the time when the film was brought intocontact with a first guide roll by conveyance was set to be 170 seconds.An arbitrary point on the film was impregnated in the swelling bath for173 seconds in total.

Comparative Example 1

A polarizing film and a polarizing plate were formed in the same manneras in Example 1. However, in this example, in a swelling treatment, alength of time (a) between the time when a film was brought into contactwith a solvent in a swelling bath and the time when the film was broughtinto contact with a first guide roll by conveyance was set to be 14seconds, and a length of time (b) between the time when the film wasbrought into contact with the first guide roll and the time when thefilm was brought into contact with a second guide roll was set to be 75seconds. An arbitrary point on the film was impregnated in the swellingbath for 94 seconds in total.

Comparative Example 2

A polarizing film and a polarizing plate were formed in the same manneras in Example 1. However, in this example, in a swelling treatment, alength of time (a) between the time when a film was brought into contactwith a solvent in a swelling bath and the time when the film was broughtinto contact with a first guide roll by conveyance was set to be 0.3seconds, and a length of time (b) between the time when the film wasbrought into contact with the first guide roll and the time when thefilm was brought into contact with a second guide roll was set to be 4seconds. An arbitrary point on the film was impregnated in the swellingbath for 15 seconds in total.

Comparative Example 3

A polarizing film and a polarizing plate were formed in the same manneras in Example 4. However, in this example, in a swelling treatment, alength of time (c) between the time when a film was brought into contactwith a solvent in a swelling bath and the time when the film was broughtinto contact with a first guide roll by conveyance was set to be 22seconds. An arbitrary point on the film was impregnated in the swellingbath for 24 seconds in total.

Comparative Example 4

A polarizing film was formed in the same manner as in Example 4.However, in this example, a PVA film that is the same as used forExample 5 was used, a spiral roll was used as the guide roll (in thesame manner as in Example 6), and swelling was performed at atemperature of 38° C. Further, with respect to the length of the rawfilm, a stretch ratio of stretching in a swelling bath was set to be 2.5times, and a stretch ratio of stretching in a dyebath was set to be 3.2times. Further, a length of time (c) between the time when the film wasbrought into contact with a solvent in the swelling bath and the timewhen the film was brought into contact with a first guide roll was setto be 188 seconds. An arbitrary point on the film was impregnated in theswelling bath for 191 seconds in total. However, in Comparative Example4, because of a poor running property of the film, a polarizing filmcould not be produced.

Comparative Example 5

A polarizing film and a polarizing plate were formed in the same manneras in Example 1. However, in this example, a PVA film that is the sameas used for Example 5 was used, and the temperature of a swelling bathwas set to be 32° C. Further, with respect to the length of a raw film,a stretch ratio of stretching in the swelling bath was set to be 2.8times, and a stretch ratio of stretching in a dyebath was set to be 3.5times. Further, a length of time (a) between the time when a film isbrought into contact with a solvent in the swelling film and the timewhen the film is brought into contact with a first guide roll byconveyance was set to be 15 seconds, and a length of time (b) betweenthe time when the film is brought into contact with the first guide rolland the time when the film is brought into contact with a second guideroll was set to be 5 seconds. An arbitrary point on the film wasimpregnated in the swelling bath for 21 seconds in total.

(Method of Evaluating Display Unevenness)

Each of the polarizing plates obtained in Examples 1 to 9 andComparative Examples 1 to 3 and 5 was cut into a square of 25 cm inlength and 20 cm in width, and a resultant polarizing plate was attachedto a surface (on a light source side) of a high-contrast type IPS liquidcrystal cell using a pressure-sensitive adhesive. Further, trade nameSEG1425DU (produced by Nitto Denko Corporation) was attached to theother surface (on a viewing side) of the liquid crystal cell. Aresultant liquid crystal panel was placed on each of various backlights(A to D) that will be described later so that the polarizing plate atthe light source side (the polarizing plate formed as described above)points downward. On the viewing side of the liquid crystal panel,observation was performed from a front direction and oblique directions(30°, 45°, 60°), and unevenness that was observed in black display wasevaluated based on the following evaluation criteria. According to thefollowing evaluation criteria, each polarizing plate can be consideredas attaining an excellent effect if rated as 7 to 6, as practicallyusable if rated as 5 to 3, and as practically unusable if rated as 2 to1.

(Evaluation Criteria)

-   -   7: No unevenness is observed.    -   6: Slight unevenness is observed in a darkroom, while no        unevenness is observed in fluorescent lighting.    -   5: Unevenness is observed in a darkroom, while no unevenness is        observed in fluorescent lighting.    -   4: Unevenness is observed clearly in a darkroom, while no        unevenness is observed in fluorescent lighting.    -   3: Slight unevenness is observed in fluorescent lighting.    -   2: Unevenness is observed in fluorescent lighting.    -   1: Unevenness is observed clearly in fluorescent lighting.        (Backlight A)

FIG. 9 is a cross-sectional view schematically showing a backlight A. Asshown in the figure, in this backlight 6, a wedge-shaped light guideplate 22 with a printed rear surface was provided with a cold-cathodetube 26 and a lamp house 27, a diffusion plate 21 was disposed on anupper surface of the light guide plate 22, and a diffuse reflector plate23 was disposed on a lower surface of the light guide plate 22.

(Backlight B)

FIG. 10 is a cross-sectional view schematically showing a backlight B.As shown in the figure, in this backlight 7, a laminate of a cholestericlayer and a λ/4 plate layer was disposed on the backlight 6 shown inFIG. 9. In this case, the laminate was disposed so that a cholestericsurface (16) was on a backlight 6 side and a λ/4 plate (15) was on aviewing side. When arranging a liquid crystal cell on the backlight 7 asdescribed above, quantity of transmitted light was controlled so as tobe maximum. As the laminate of the cholesteric layer and the λ/4 platelayer, trade name PCF400TEG produced by Nitto Denko Corporation withouta polarization plate portion was used.

(Backlight C)

FIG. 11 is a cross-sectional view schematically showing a backlight C.As shown in the figure, in this backlight 8, an anisotropic multiplethin-film reflective polarizer (trade name DBEF; produced by 3M Co.) 17was disposed on the backlight 6 shown in FIG. 9. When arranging a liquidcrystal cell on the backlight 8 as described above, quantity oftransmitted light was controlled so as to be maximum.

(Backlight D)

FIG. 12(A) is a cross-sectional view schematically showing a backlightD, and FIG. 12(B) schematically shows a partial view of FIG. 12(A). Asshown in the figure, in this backlight 9, a wedge-shaped light guideplate 25 had a light-emitting surface on which a prism was formed, andwas provided with a cold-cathode tube 26 and a lamp house 27, a diffusereflector plate 23 was disposed on a lower surface of the light guideplate 25, and a prism sheet 24 was disposed on an upper surface of thelight guide plate 25. As shown in FIG. 12(B) showing a partiallyenlarged view of FIG. 12(A), this prism sheet 24 was disposed so thatits prism surface faced a prism surface of the light guide plate 25. Adiffusion plate 21 further was disposed on an upper surface of the prismsheet 24. TABLE 1 Backlight A Backlight B Backlight C Backlight D 0° 30°45° 60° 0° 30° 45° 60° 0° 30° 45° 60° 0° 30° 45° 60° Ex. 1 7 7 7 7 7 7 77 7 7 7 7 7 7 7 6 Ex. 2 7 7 7 6 7 7 6 5 7 7 6 6 7 7 6 6 Ex. 3 7 7 6 6 76 6 5 7 6 5 5 7 7 6 5 Ex. 4 7 7 7 7 7 7 7 7 7 7 7 7 7 7 6 6 Ex. 5 7 7 77 7 7 7 7 7 7 7 7 7 7 7 7 Ex. 6 6 6 6 5 6 5 4 4 6 5 4 4 6 6 5 5 Ex. 7 77 7 7 7 7 6 6 7 7 6 6 7 7 7 6 Ex. 8 7 7 6 6 7 7 6 5 7 7 6 6 7 7 6 6 Ex.9 7 7 7 7 7 7 7 6 7 7 7 6 7 7 6 6 Com. Ex. 1 4 4 4 3 4 3 3 2 4 3 2 1 4 32 2 Com. Ex. 2 3 3 3 2 3 2 1 1 3 1 1 1 3 3 2 2 Com. Ex. 3 3 3 2 2 3 2 21 3 2 1 1 3 3 2 1 Com. Ex. 4 — — — — — — — — — — — — — — — — Com. Ex. 53 2 2 1 2 1 1 1 2 1 1 1 3 2 1 1

As is apparent from Table 1, compared with the polarizing plates ofComparative Examples 1 to 3 and 5, the polarizing plates of Examples 1to 9 exhibited an excellent effect that display unevenness when viewedfrom the front and obliquely was reduced. These results show that theproduction method according to the present invention allows an excellentpolarizing film to be produced, and thus it is made possible to providevarious image displays in which display unevenness is suppressed.

INDUSTRIAL APPLICABILITY

As described in the foregoing discussion, when a polarizer produced bythe production method according to the present invention is used in aliquid crystal panel, a liquid crystal display or the like as an opticalfilm such as a polarizing plate or the like, display unevenness can beeliminated, thereby achieving excellent display characteristics.Furthermore, according to the present invention, a polarizer, apolarizing plate or the like can be provided with markings by in-linemeasurement. Therefore, for example, off-line processes such as visualinspection immediately after performing chip-cutting of the polarizer,packaging and the like become unnecessary, allowing a total in-houseproduction of attaching the polarizer to a liquid crystal display or anEL display. This achieves, for example, a cost reduction of the display,and makes it easier to control its production processes, thus providinggreat industrial significance.

1. A method of producing a polarizing film, comprising the steps of:allowing a hydrophilic polymer film to swell wherein the polymer film isconveyed by means of a guide roll so as to be impregnated in an aqueoussolvent in a swelling bath; dyeing the polymer film using a dichroicsubstance; and stretching the polymer film, wherein in the swellingstep, at least a first guide roll and a second guide roll are arrangedin the swelling bath, and when the polymer film is impregnated in andallowed to travel in the aqueous solvent, the polymer film is broughtinto contact with the first guide roll within a time up to when swellingreaches a saturation state and further is brought into contact with thesecond guide roll after the swelling reaches the saturation state. 2.(canceled)
 3. The method according to claim 1, wherein a required lengthof time (a) between the time when the polymer film is brought intocontact with the aqueous solvent and the time when the polymer film isbought into contact with the first guide roll is 0.6 to 12 seconds. 4.The method according to claim 1, wherein a required length of time (b)between the time when the polymer film is brought into contact with thefirst guide roll and the time when the polymer film is brought intocontact with the second guide roll is 13 to 120 seconds.
 5. The methodaccording to claim 4, wherein a total length of time of the requiredlength of time (a) and the required length of time (b) is in a range of25 to 180 seconds.
 6. A method of producing a polarizing film,comprising the steps of: allowing a hydrophilic polymer film to swell inan aqueous solvent, in which the polymer film is conveyed by means of aguide roll so as to be impregnated in a swelling bath of the aqueoussolvent; dyeing the polymer film using a dichroic substance; andstretching the polymer film, wherein in the swelling step, at least afirst guide roll is arranged in the swelling bath, and when the polymerfilm is impregnated in and allowed to travel in the aqueous solvent, thepolymer film is brought into contact with the first guide roll afterswelling reaches a saturation state.
 7. The method according to claim 6,wherein a required length of time (c) between the time when the polymerfilm is brought into contact with the aqueous solvent and the time whenthe polymer film is brought into contact with the first guide roll is 25to 180 seconds.
 8. The method according to claim 1, wherein a length oftime in which the polymer film is impregnated in the swelling bath isnot less than 100 seconds.
 9. The method according to claim 1, whereinthe hydrophilic polymer film before being subjected to a swellingtreatment has a thickness in a range of not more than 110 μm.
 10. Themethod according to claim 1, wherein the hydrophilic polymer film is apolyvinyl alcohol-based film.
 11. The method according to claim 1,wherein the hydrophilic polymer film contains a plastic material in anamount of 1 to 17 wt %.
 12. The method according to claim 1, wherein theguide roll is at least one selected from a crown roll, a bent roll, anda roll with lugs.
 13. The method according to claim 1, wherein a guideroll other than the first guide roll comprises a spiral roll.
 14. Themethod according to claim 1, wherein a temperature of the swelling bathis in a range of 15 to 50° C.
 15. The method according to claim 1,wherein in the swelling step, the polymer film is subjected to a furtherstretching treatment in the swelling bath.
 16. The method according toclaim 1, wherein with respect to a length of the polymer film beforebeing subjected to the swelling step, a stretch ratio of the polymerfilm in the stretching treatment is in a range of 1.5 to 4.0 times. 17.The method according to claim 1, wherein the dichroic substance is atleast one of iodine and organic dyestuffs.
 18. The method according toclaim 17, wherein the dichroic substance comprises at least two of theorganic dyestuffs.
 19. A polarizing film produced by a method as claimedin claim
 1. 20. An optical film comprising a polarizing film, whereinthe polarizing film is a polarizing film as claimed in claim
 19. 21. Theoptical film according to claim 20, wherein the optical film furthercomprises a transparent protective layer, and the transparent protectivelayer is disposed on at least one surface of the polarizing film. 22.The optical film according to claim 20, wherein a pressure-sensitiveadhesive layer is provided in at least one outermost layer of theoptical film.
 23. The optical film according to claim 20, wherein theoptical film further comprises at least one of a polarization convertingelement and a retardation film.
 24. The optical film according to claim23, wherein the polarization converting element is an anisotropicreflective polarization element or an anisotropic scatteringpolarization element.
 25. A liquid crystal panel, comprising: apolarizing film as claimed in claim 19; and a liquid crystal cell,wherein the polarizing film is disposed on at least one surface of theliquid crystal cell.
 26. A liquid crystal display comprising a liquidcrystal panel as claimed in claim
 25. 27. The liquid crystal displayaccording to claim 26, wherein the liquid crystal display includes aflat light source that emits polarized light.
 28. An image displaycomprising a polarizing film as claimed in claim
 19. 29. The imagedisplay according to claim 28, wherein the image display is anelectroluminescence display.
 30. An in-house production method forproducing an image display as claimed in claim 28, comprising a step inwhich the polarizing film is attached to the display immediately afterbeing subjected to chip-cutting.